Hard disk apparatuses and optical disk apparatuses are equipped with a motor for rotating a disk. A motor is described in, for example, JP-A 2002-339955. The motor described in JP-A 2002-339955 includes a dynamic bearing. The dynamic bearing includes a rotating shaft, a supporting member, and a lubricating oil interposed between the rotating shaft and the supporting member. The rotating shaft is arranged to rotate with respect to the supporting member in a non-contact state. The rotating shaft has a through hole sealed with a sealing screw. This prevents intrusion of the lubricating oil into the through hole.
According to the structure described in JP-A 2002-339955, a disturbance is caused in assembling or driving the motor, so that stress is applied to the shaft (rotating shaft). As a result, there is a possibility that the lubricating oil enters the shaft due to the deformation of the shaft, and other reasons. In addition, when a shaft having an excessively large diameter is used for the purpose of securing the stiffness of the shaft, a size of a motor including this shaft is increased.